The present invention relates to a display device, and, more particularly, relates to a display device for displaying, by the movement of an indicating member, the value of some quantity. Such a display device is particularly well adapted for display of the transmission shift range in which an automatic transmission fitted to a vehicle is set.
In automobiles which are equipped with automatic transmissions which are controlled by a controlling shift lever mounted upon a steering column outer tube, so that by the use of this selecting lever the automatic transmission may be selected between, for example, "L", "2", "D", "N", "R" and "P" ranges, it is well known for an indicating device or dial type indicator to be fitted and coupled to the movement of said controlling shift lever, so as to indicate to the operator of the vehicle in what range the transmission is set. Such a display device is usually fitted on the upper side of a steering column which is located in a slanting orientation in the vehicle, so that the display device is upwards and to the front of the steering column outer tube, from the point of view of the driver. In other words, such a display device is located in the direction towards the instrument panel of the vehicle from the steering column outer tube. This is a good location to allow for easy viewing of the display device by the driver, during operation of the vehicle.
Conventionally, such an automatic transmission range display device is provided with an indicator member, which is rigidly coupled to the aforesaid shift lever which is used for shifting said automatic transmission between its various speed ranges, and which is pivoted around its own axis. Cooperating with this indicator member, a display plate inscribed with symbols denoting shift ranges, such as "L", "2", "D", "N", "R", and "P", is arranged, so that the indicator member of the display device indicates one of these range symbols, in order to show to the driver in which shift range the automatic transmission is currently set and operating. Thus, as the transmission is shifted between its various shift ranges by use of the selecting lever, i.e., as this lever is rotated around its axis, the indicator member moves between these shift range indicating symbols on the display plate. Therefore, according to the rotational position of the indicator member, one or another of these symbols is picked out.
In a display device, generally, it is preferable that the symbols indicated by an indicating member of the display device should be arranged sufficiently far apart to be easily picked out, even from quite a distance, by the operator of a vehicle or other device to which the display device is fitted. That is to say, if the symbols on the display device are located too close together, in other words, if the range of movement of the indicating member between the various positions which it is capable of assuming is too small, then it will be difficult to read the display device.
The distances between various indicating symbols which are designated by different positions of an indicator member which rotates about an axis are proportional, both to the angles through which the indicator member is rotated about said axis, and to the distance from said axis of the portion of the indicator member which is brought proximate to said indicating symbols. Thus, in order to increase the distance between said symbols, it is desirable either to increase the angle through which the indicator member is moved, or to increase the length of the indicator member from said axis. However, since in a conventional indicating device, as described above, the indicator member is directly driven by the selecting lever or control shaft, therefore the rotational angle through which this indicating member is moved is limited to be the same as the angle through which this selecting lever is moved, and in the case of an automatic transmission is limited by the construction of the automatic transmission and of the linkage of the selecting lever thereto. Further, in an actual vehicle, the range of motion through which said selecting lever may be moved is often quite limited, since otherwise the selecting lever may interfere with other parts of the vehicle, or with the body of the driver.
Therefore, the angle through which such an indicator member may be moved may well be rather restricted. In order to obtain good separation of the indicating symbols on such a display device, therefore, it is desirable to increase the length between the axis of such an indicator member, around which is rotates, and the portion of the indicator member which is brought proximate to the various indicating symbols. However, because of the general positioning in automobiles of a steering column outer tube as obliquely upright and close to the front of a vehicle, and because of the convenience of positioning such a display device forward and upward of the steering column outer tube, the space available for such a display device is much restricted, and it may not be possible to increase the effective radius of an indicator member, i.e. the distance between the axis of rotation of said indicator member and the tip thereof which is proximate to said indicating symbols of the display device,. Therefore a difficulty has arisen with aforesaid prior art display device constructions, in that, because the various indicating symbols thereof are necessarily located rather close together, they are small and hard to read, especially in poor lighting conditions.
This problem is particularly acute in cab-over type, i.e. foward-control type, automobiles and trucks, in which the driver is seated very close to the front of the vehicle, and the steering column outer tube is oriented nearly vertically, so that there is very little room in front of said steering column outer tube, between it and the dash panel of the vehicle. Especially in such vehicles, the indicator member cannot be made very lon, due to the restricted space available for the display device. Thereby, the intervals between the various transmission range indicating symbols are reduced to such an extent that it is very difficult to distinguish between them.